1. iPhone / iPAD USB connection
There is no possibility to use USB on iOS. Apple does not allow developers to use USB.
Only WiFi (built-in or mobile WiFi router like TP-Link MR3040) connection can be used.

2. Android USB connection
It is only possible if the Android device has the USB host function.
You can use this free application to check if your Android device has the USB host function: https://play.google.com/store/apps/deta ... iagnostics
If your Android device has the required USB host function you can use an USB OTG adapter to connect your DSLR (Nikon, Canon) with USB
Some useful info on USB OTG adapters: https://android.stackexchange.com/quest ... tg-support
In qDslrDashboard settings enable the 'Use Android native USB access' option.
With qDslrDashboard V3.5.8 you can also try with the 'Use Android native USB access' option disabled.

3. Video recording with Canon/Nikon DSLR
Only with USB (direct or WiFi router).
Nikon D500/Z6/Z7 supports video recording in wireless mode.
Cannot be done when connected to camera built-in WiFi - it's a camera limitation and has nothing to do with qDD.

4. Nikon D3x00 no video recording
Nikons D3x00 does not have ability to record video with remote control.
You can record video only from camera and it cannot be connected for remote control

5. Nikon DSLR LiveView on camera and qDD
Nikon does not allow to see LV on camera when camera is connected with USB and the camera controls are disabled by camera (remote release also not working while in live view)

6. Automatic video recording restart
For now there is no such function

7. Connecting more remote devices to one camera
For now there is no such possibility. Cameras allow only one device connected.

9. Will camera X be supported ??
If it has API/SDK or documentation for developing remote control it might (currently Fuji, Panasonic, Olympus does not release any documentation for developers and because of this these models are currently not supported).
For now only Nikon, Canon DSLR have availabe SDK's. And Sony has API for "Smart Remote control" app and only WiFi connection is available.

10. Will qDslrDashboard/ControlMyCamera work with a wifi SD card?
No, wifi SD cards are not support and will not be supported as it does not allow controlling the camera

12. qDslrDashboard/ControlMyCamera can't connect to the camera over wireless
On some newer phones when mobile data is active qDslrDashboard / ControlMyCamera can't connect to the camera wireless so the solution is to turn off the mobile data for that period.

D3000, D3100, D3200, D3300, D3400 - cameras have limited remote functionality and only basic control is available. There is no BULB, no video recording, no AF point change in LV, and no many other functions.